Apparatus for producing an air curtain



Nov. 17, 1964 w. TAMM ETAL APPARATUS FOR PRODUCING AN AIR CURTAIN 9Sheets-Sheet 1 Filed Aug. 1, 1961 FIG'J WALTER TAMM WERNER KNAPPINVENTORJ .Nov. 17, 1964 w. TAMM ETAL APPARATUS FOR PRODUCING AN AIRCURTAIN 9 Sheets-Sheet 2 Filed Aug. 1. 1961 WALTER TAMM WERNER KNAPPINVENTORS m9 o m: H wow or mu Nov. 17, 1964 I W. TAMM ETAL APPARATUS FORPRODUCING AN AIR CURTAIN 9 Sheets-Sheet 3 Filed Aug. 1. 1961 WALTER TAMMWERNER KNAPP INVENTORS O O O O 0 0 0 0 0 0 0 O O O O OOOOOOOOO Nov. 17,1964 w. TAMM ETAL APPARATUS FOR PRODUCING AN AIR CURTAIN 9 Sheets-Sheet4 Filed Aug- 1. 1961 WEI TER TQM/t7 wERA EZ K HP Nov. 17, 1964 w. TAMMETAL APPARATUS FOR PRODUCING AN AIR CURTAIN 9 Sheets-Sheet 5 Filed Aug.1, 1961 4 7- TaQA/E/ Nov. 17, 1964 w. TAMM ETAL 3,157,105

APPARATUS FOR PRODUCING AN AIR CURTAIN Filed Aug. 1, 1961 9 Sheets-Sheet6 I ll M/ VENTQQS Nov. 17, 1964 w. TAMM ETAL 3,157,105

APPARATUS FOR PRODUCING AN AIR CURTAIN Filed Aug. 1, 1961 9 Sheets-Sheet7 WALTER TAMM WERNER KNAPP INV EN TORS Nov. 17, 1964 w. TAMM ETAL3,157,105

APPARATUS FOR PRODUCING AN AIR CURTAIN Filed Aug. 1, 1961 9 Sheets-Sheet8 WERNER KNA PP WALTER TAMM INVENTORS Nov. 17, 1964 w. TAMM ETAL3,157,105

APPARATUS FOR PRODUCING AN AIR CURTAIN Filed Aug. 1, 1961 9 Sheets-Sheet9 W444 122 7 7mm fi WEZA/EZ 41/4 9 ,q 7- ramusy out its range ofadjustability.

United States Patent 3,157,105 APPARATUfi FQR PRQDUCENG AN Am CURTAENWalter Tarnm, Georgenstrassefiai, Munich, Germany, and Werner Knapp,Fcderburgstrasse 59, Ravensburg, Germany Filed Aug. 1, 1961, Ser. No.128,592 12 (Claims. (til. as-se) The present invention relates to anapparatus for restricting air convection between two spacesinterconnected by a wall opening, eg. the interior and the exterior of abuilding, by screening such opening with the aid of a curtain of airpassing across the opening.

It is the object of our invention to provide improved means forproducing air curtains of the character described to screen openingscommunicating between regions of chambers of air at markedly differenttemperatures whereby cool air may be prevented from entering a eatedchamber and warm air from entering a cooled chamber. We have found thatconventional air curtains are defiectedat least at the lower portion ofthe opening by a convection current of cool air moving toward the regionof higher temperature and rising from the higher density of the coolair. Thus, the air in a cold chamber at C. is about 13% more densethanthe external air, which is at a temperature of, say, +20 C., andconsequently the pressure exerted by a column of cold air 2.5 metershigh in the chamber exceeds by about 6.53 kg./ m. that of a column ofthe warmer air of the same height. It is, accordingly, a feature of ourinvention to provide an air-curtain-producing apparatus adapted toscreen such openings with a curtain of air directed preferablydownwardly thereacross at an adjustable slight angle of, say, 15 tothereby deflecting a preferably minor portion of the stream incounter-curreut to the aforementioned convection current of cool air andcounterbalancing the normal pressure gradient across the opening. An aircurtain so oriented will deflect a stream or entering air to produce asecondary circulation in the region of the opening between twotransverse limiting surfaces such as, for example, the ground and aledge forming a seal between the wall and the source of air flowsupported thereon. This source, in turn, should include a plenumchamber, supplied with air from one or more blowers, and an elongatednozzle communicating with it, the nozzle having as its outlet anelongated slot extending along an edge of the usually rectangular wallopening. In order to insure the existence of the aforementioned ant ls,the nozzle is advantageously defined, along the major sides of the slot,by two panels having the desired inclination with respect to theadjacent wall surface. A system of this description has been disclosedin our copending application Ser. No. 706,171, filed December 30, i957,and now abandoned, of which the present application is acontinuation-'in-p art; 1

Devices of this character have proved themselves use ful not only atbuilding doors and windows but also, to an ever-increasing extent, onmobile equipment such as refrigerated trucks. In many instances a.highly compact arrangement is called for along with some mechanism foreffectively controlling the flow of air under different operatingconditions. It is, therefore,,a furt er object of the present inventionto provide simple and dependable means for maintaining an optimum rateof air flow in such devices and, preferably, for enabling adjustment ofthis r ate witlL'n wide limits. A more particular object of theinevntion is to provide means for equalizing the flow rate over theentire length ofthe nozzle through Advantageously, the apparatusaccording to our invention has not only means for controllins thequantity of air Q and the velocity V thereof in forming the air curtain,out also means for adjusting the angle ,8 between the plane of thescreened opening and the nozzle of the apparatus and, consequently, forsetting the complementary impact angle 0: between the impinging aircurtain and ground or ledge. The. air curtain, upon impact, divides intoa forward stream generally directed toward the warm region and arearward stream which establishes the secondary circulation tocounterbalance the effect of the cold-air convection current. We havefound that optimum screening results, for openings between regionshaving the usual temperature differentials (e.g. 20 to 50 C.)therebetween, may be obtained when the ratio of the flow rates Q and Qof the rearward and forward streams is equal to about 1/2. Since thefiow-rate ratio may be given by the expression the angle or will befound to have a value of about 20 although the optimum angle for eachinstallation may have to be determined by the particular conditionspreseat at the screened opening. in general, We have found that theangle or should be equal to about 20i5.

Although the optimum selection of the other air-curtain parameters, eg.nozzle width and flow rate, may also be determined individually for eachinstallation, highly satisfactory air curtains were obtained withnozzles 20 to 30 mm. in width and flow rates from 8 to 12 meters persecond to screen out cold air; with nozzles up to 60 mm. in width andhow rates from 12 to 18 meters per second to screen out Warm air,breezes and, occasionally, high winds; and with nozzle widths from tomm. and flow rates of 15 to 20 meters per second for air curtainsadapted to repel insects from an opening.

It should be noted further that the lower the speed at which theair-curtain stream impinges upon the opposite Wall or ledge, the smalleris the quantity of air which constitutes the rearward stream. When theair-curtain flow rate is reduced below a predetermined value, determinedby the conditions (e.g. temperature) present at the opening, no rearwardstream is able to flow countercurrent to the convection-current streamat the base of the opening and to provide a balancing effect therefor.There are, however, limits to the'maximum and minimum values of theimpact an le and to the flow rate of the aircurtain stream. For example,the smaller the impact angle or is made, the larger will be theunprotected triangular area between the main air-curtain stream and theplane of the opening, thereby decreasing the effectiveness of thecurtain since screened-out air tends to penetrate the air curtain viathis unprotected region.

It is, therefore, another feature of the invention to provide means forsetting the nozzles of the air-curtain-producing apparatus at thecorrect angle and to control the flow of air therethrough, therebyenabling the apparatus to be used equally well for openings ofrelatively low height where relatively low flow rates are desirable andfor relatively high openings where high flow rate are required.Generally, an opening of reduced height will require an apparatus havinga smaller nozzle angle than an apparatus employed for air-curtainscreening of higher openings.

A further feature of the invention resides in the provision of means forscreening the lateral portions of the aforementioned triangular region,included between the main air-curtain stream and the plane of theopening, by secondary air curtains, thereby preventing the penetrationof screened-out air through the air curtain via this region.

in order to reinforce the secondary stream of the air curtain, whichgenerally flows toward the cooler region,

a the air-curtain-produciug apparatus may be provided with Venturi-typeaspirating means, e.g. a tube communicating with the interior of thenozzle and the space defined by the latter, the building-wall portionsadjacent the opening and the sealing or baffle means in the gap betweenthe nozzle and the wall, adapted to accelerate the secondary stream.While it is usually preferable to dispose the air-curtain apparatusabove the opening to be screened within the warm region, we have foundthat space-saving considerations, especially for screened openings ofrefrigerated vehicles, often require the positioning of the apparatuswithin the cooled area in which case the primary air-curtain stream isdirected in counter-current to the convention current of cool air towardthe opening. To minimize the excess of the primary stream over theconvention current, the impact angle of the main aircurtain flow is setas close to 90 as is practical. More over, it frequently is desirable toposition a pair of such air-curtain-producing devices along eachvertical edge of a generally rectangular opening whereby the nozzles ofthe two devices direct opposing air-curtain streams toward the medianplane of the opening. While the opposing streams may be designed tomerge at a straight angle (i.e. 180) whereby substantially equal forwardand rearward streams may be established, it is preferable that the twoair-curtain streams include an angle less than 180 whose vertex isdirected toward the warmer region, thereby resulting in a forward streamwhose flow rate may be in the aforementioned desirable ratio of 2:1 tothe flow rate of the rearward stream.

In accordance with another aspect of this invention there is provided,in an air-curtain-producing apparatus of the character hereinabovedescribed, a tubular element open at one or both ends, defining a plenumchamher, which is formed on one side with a longitudinal slot extendingover a major part of its length, this slot terminating in a nozzleextending substantially tangentially of the tubular element whereby airadmitted under pressure from the open end or ends is deflected sidewaysand then outwardly through the nozzle; between the source of air and theplenum chamber proper, i.e. the region defined by the longitudinal slot,there is formed within the tubular element a generally cylindrical spaceor antichamber free from internal obstructions whose axial length issufficient to enable the turbulent incoming air to revert to laminarflow. This axial length is advantageously of the order of the width ofthe element, or at least as large as its radius, and may in practicerange between about 10 and 25 cm. with tubes of 20 to 40 cm. indiameter. The plenum chamber beyond this space is preferably provided,according to a further feature of the invention, with guide means partlyobstructing the air flow through the slot whereby a substantial part ofthe air is deflected further along the tube so as to pass through thenozzle at locations remote from the inlet; in this manner the velocityof the outflowing air can be substantially equalized over the length ofthe plenum chamber. The guide means may comprise a set of axiallyspaced, laterally offset baflies within the tube or, in simpler cases, aperforated screen spanning the slot.

We have found, in this connection, that the velocity of the outflowingair can be substantially equalized over the length of the nozzle in theabsence of such bafiies under certain conditions although, even undersuch circumstances, it is advisable to use the battles to insure aminimum velocity gradient from the portion of the nozzle proximal to theinlet of the plenum chamber to the portions of the nozzle remotetherefrom. More specifically, we have determined that the ratio V /V ofthe velocity V of the outlet air at a location of the elongated nozzleremote from the closed end of the plenum chamber to the velocity V ofthe outlet air at a location proximal thereto is proportional to \/1+(cl/A) where ((1/11) is the ratio of the outlet cross-sectional area ato the cross-sectional area A of the inlet to the plenum chamber. Thus,the maximum gradient between the velocities V and V may be maintainedbelow any desired value by a suitable dimensioning of the inlet andoutlet cross-sectional areas; for instance, if, as is generally thecase, the velocity V ranges from V V to V =l.l V the ratio (a/A) will befound to range from a/A=0 to about a/A==0.48.

Advantageously, a plurality of angularly adjustable transverse plates,which function as dampers, may be spacedly positioned along theelongated mouth of the nozzle to provide a final means for adjusting thevelocity of the outlet air therealong and for correcting the directionof flow of the outlet air. These dampers may be independently adjusta heor provided with common actuating means for regulating the air outflow.The outlet tip of the nozzle may, according to a more specific featureof the invention, be angularly displaceable about an axis parallel toits major dimension to permit correction of the angle of impact. We havealso found that, when nozzles extending substantially tangentially froma plenum chamber are employed, air turbulence in the region wherein thetangential nozzle opens into the cylindrical plenum chamber may beobviated by the provision of a deflecting strip extending from thecommon inner wall of nozzle and plenum chamber into the latter andincluding with the plane of the nozzle an angle of about 20 to 40.

The above and other objects, features and advantages of the inventionwill become more fully apparent from the following detailed description,reference being made to the accompanying drawing in which:

FIG. 1 is a perspective view of an air-curtain-producing apparatusembodying the invention;

FIG. 2 is a side view of the apparatus (parts broken away) taken on theline II-II of FIG. 3;

FIG. 3 is a cross-sectional view taken on the line llilii of FIG. 2;

FIG. 4 is a view (parts broken away) of the left-hand portion of FIG. 2,drawn to a larger scale and illustrated in a ditferent position ofadjustment of its inlet-control mechanism;

FIG. 5 is a cross-sectional view taken on the line VV of FIG. 4;

FIG. 6 is a view similar to FIG. 2, showing a modified embodiment;

PEG. 7 is a cross-sectional view taken on the line VlIVlI of FIG. 6;

FIG. 8 is a side-elevational view, partly in section, of the nozzle ofan air-curtain-producing apparatus provided with aspirating meansaccording to the invention;

FIG. 8A is a front-elevational view, partly in section, of the apparatusshown in FIG. 8;

FIG. 9 is a view similar to FIG. 8 of a nozzle according to anotherembodiment of the invention;

FIG. 10 is a side-elevational view of an air-curtainproducing apparatusillustrating means for adjusting the angle included between its aircurtain and the plane of the screened opening;

FIG. 11 is a view similar to FIG. 10 of an apparatus having a registerdisposed at the base of the opening below its nozzle for deflecting theair stream;

FIG. 12 is a perspective front view of an apparatus whose air intake hasan axis parallel to the nozzle;

FIG. 13 is a front-elevational view of an apparatus Whose air intake hasan axis extending transversely to the elongated nozzle;

FIG. 14 is a cross-sectional view taken along the line XIVX1V of FIG.13;

FIG. 15 is a front-elevational view, partly in section, of an apparatuswhose plenum chamber is supplied with air via two tangential blowers;

FIG. 16 is a view similar to FIG. 15 of another apparatus in which theblower means are disposed within the plenum chamber;

FIG. 17 is a cross-sectional view taken along the line XVII-XV1I of FIG.16;

FIGS. 18-21 are side-elevational views of air-curtainproducing devicesaccording to further embodiments of the invention, illustrating theoperation thereof somewhat schematically;

FIG. 22 is a view similar to FIG. 7 of a plenum chamber and itstangential nozzle, showing additional means for suppressing turbulence;

FIG. 23 is a cross-sectional view taken along line XXIII-XXIII of FIG.22;

FIG. 24 is a front-elevational view of a wall opening provided withlateral air-curtain-producing devices;

FIG. 25 is a cross-sectional view taken along the line XXVXXV of FIG.24;

FIG. 26 is a view similar to FIG. 24 of an opening having anair-curtain-producing apparatus thereabove and provided withsupplemental means for preventing the flow of air between the chambersinterconnected by the opening according to another embodiment of theinvention;

PEG. 27 is a cross-sectional view taken along line XXVIL-XXVII of FIG.26;

FIG. 28 is a perspective front view of an air-curtainproducing apparatuswhose inlet axis extends transversely to the nozzle;

FIG. 29 is a front-elevational view of a slightly modified apparatus;and

FIG. 30 is a side View of the apparatus of FIG. 29.

As shown in FIG. 1, an air-curtain-producing apparatus 101 is fastenedupon a vertical wall 131, above an opening 132 therein, by means ofbrackets (not shown) engaging lugs 130, 130" of which several pairs areprovided at diiierent peripheral locations to afford a choice ofmountings. The apparatus 101, of generally tubular elongated shape, isprovided on one end with an adjustable air intake 105 having a portscreened by a mesh guard 106 for the admission of an air flow at a ratecontrolled by an adjusting mechanism 120. An elongated nozzle 127 has anoutlet slot 137 and slants downwardly from the cylindrical main part 102of the apparatus. Air issues from the nozzle 127 at high speed, the mainair stream forming an angle 13 with the wall 131. Depending upon variousconditions, such as the dimensions of nozzle 127 and the temperaturegradient in opening 132, the optimum angle of incidence u. for achievingthe best screening effect may vary between approximately and 25 aspreviously noted, the complementary impact angle ,8 between theimpinging air stream and ground being therefore about 65 to 75. Thespace between wall 131 and the diverging lower end of nozzle 127 issealed by a packing 129.

The air intake 105 of the apparatus 101 comprises, as shown in FIGS. 2,4 and 5, in a head 111 restrictedly rotatable on the hollow cylinder 102whose interior defines a plenum chamber 103 and an antechamber 128. Aplurality of vanes 107 made of mild steel or other convenient material,e.g. sheet aluminum, are spot-welded to sleeves 109 swingable aroundarms 110, the latter extending radially from a central boss 103. Anyconvenient number of vanes may be provided, eight being shown in theillustrated embodiment. The inner end of each sleeve 109 has welded toit a bent lug 112 which extends through a slot 113 in a disk 114 rigidlyattached (e.g. by welding) to a central support shaft 115 traversing theboss 103. The shaft 115 is carried by a spider 116 having a plurality ofbars whose outer ends are welded to cylinder 102 from the inside. On itsend remote from disk 114 the shaft 115 supports a fan constituted by anelectric motor 117 baring blades 118 (FIG. 4).

The arms 110 extend radially to the intake head 111 to which the outerends of the arms are attached by bolts 119. On its circular edgeembracing cylinder 102, head 111 supports a rack 121 bearing a graduatedscale. A worm 122 mounted on a shaft 123 engages the rack 121, and apointer 124 registers the relative angular displacement of head 111 andcylinder 102 on the scale, thereby also indicatingthe degree of openingof the air intake 105. Shaft 123, journaled in bearings 1Z5, terminatesat one end in a milled knob 134. The mesh guard 106 is fastened to theair intake by means of cleats 126.

The fan forces air from the entrance port of intake 105 into the plenumchamber 103 and expels it through the nozzle 127. As shown in FIG. 3,the nozzle 127 is tapered to provide a constriction which concentratesthe air flow to produce a downwardly directed jet. The air on thedownstream side of the fan 118 is turbulent, hence the antechamber 128is formed as a free space devoid of bafiles and projections so that theair flow is smoothened when passing through this section. The plenumchamber 103, on the other hand, is provided with axially spaced andlaterally ofiset bafiles 133a, 1331), 133a, 133d which direct the outletair into the nozzle 127. In order to insure an equal exit velocity alongthe whole length of the duct 127, the plenum chamber 103 is divided bythe battles 133a to 133d into compartments of equal crosssectionalareas; for this purpose the centrally located bafiies 133b, 1330 arenearer to each other than to the outer bafdes 133a, 133d. As a result ofthis arrangement the air velocity prevailing in the compartments definedby the bafiles is substantially uniform.

As shown in FIG. 3, the upstream edges of the baffles 133a to 133d areinclined to the vertical; each bafile comprises a curved downstreamportion which directs the air from plenum chamber 103 into the nozzle127 and merges with an upstream portion extending longitudinally of theplenum chamber. Advantageously, the proximal edge of at least one baffielies at the junction of antechamber 123 and plenum chamber 103 as hereshown for the battle 133a.

It has been found that with plenum chambers arranged in this manner itis possible to minimize any variations in the velocity of the airleaving the plenum chamber at different points, the maximum velocityvariation being 5% of the mean velocity.

In FIG. 2 the vanes 107 are shown in a fully closed position, therebyobstructing the flow of air into the plenum chamber 103. The vanes 107can be moved in unison from this position toward a partly or fully openposition, as shown in FIGS. 4 and 5, by causing a relative rotationalmovement between the intake head 111 and the cylindrical chamber housing102 by means of the adjusting mechanism operated by knob 134. Rotationof the arms 110 connected to the head 111 causes the lugs 112 toco-operate with the slots 113 in disk 114 to rotate the vanes 107 ontheir sleeves 100 around the arms 110 into the open position. The disk114 does not move because it is rigidly fixed to shaft 115.Advantageously, the disk is somewhat resilient or covered by a. softelastic layer to cushion the impact of the vanes 107 upon closure. 7

It is, therefore, possible to move the vanes 107 from their coplanarclosure position (FIG. 2) through a continuity of intermediate positions(FIGS. 4 and 5) into a fully open position, in which the air flowthrough the intake is substantially unimpeded, and vice versa.

In the modification illustrated in FIGS. 6 and 7 the baffles aredispensed with, and in their place there is arranged a perforatedpartition 133' located between the plenum-chamber housing 1 3. and thenozzle 127 while extending along the entire length of the nozzle. Thepartition has the effect of distributing the air pressure so thatthroughout the length of the duct 127 the air velocity will again besubstantially uniform. The device 101' shown in FIG. 6, centrallysubdivided by a partition 1 11, has two oppositely positioned airintakes 105', 105" Whose heads 111, 111" are jointly controlled by athermostatic device to regulate the rate of inflow. Evidently, asymmetrical arrangement such as that shown in FIG. 6 may also be usedfor the type of device illustrated in FIGS. 1-5, particularly withplenum chambers of great length.

In FIG. 8 we show an air-curtain-producing apparatus whose plenumchamber feeds air to a nozzle 4, mounted upon a wall 7 above an opening1 therein. A suitable sealing means in the form of a resilient packingis disposed between the nozzle 4 and the wall 7 and forms therewith adownwardly open space as illustrated, for example, in FIG. 20. Asclearly though somewhat diagrammatically shown in the latter figure andin FIGS. 18, 19 and 21, the nozzles 4 and 4 (FIG. 19) include angles {3with the plane of the opening 1 whereby the air-curtain streams 5,issuing from the nozzles, includes a complementary impact angle a withthe floor 6 and, upon impact, forms the aforementioned primary streamand a secondary circulation 9 of air. The latter comprises a streamextending along the floor 6 in counter-current to any cool air fiowalong the latter from the cooler chamber A (FIG. 18) toward the warmerchamber B. The circulating stream 9 is deflected upwardly within thecooler chamber A whence it returns to the nozzle 4, 4' to becomeentrained by the downwardly flowing air curtain.

Whereas in the embodiment illustrated in FIG. 18 the apparatus includingits fan 2, plenum chamber 3 and nozzle 4 is mounted directly upon thewall without any gap therebetween whereby the nozzle-forming platesserve to direct the circulating stream 9 back into the main aircurtainflow, in the embodiment of FIG. 19, which is shown to have a nozzle 4'formed with two parallel mouths adapted to produce a double-layercurtain of particular effectiveness, a resilient packing 10' is disposedbetween the nozzle and the wall 7 to prevent the accumulation ofnon-circulating air therein. Depending upon the specific operatingconditions, the packing 10' may completely fill the gap of triangularcross-section between the nozzles 4 (FIG. 19) to prevent the formationof a dead space therein or may leave therein a recess 1011 (FIG. 20),swept by the secondary circulation 9, adjacent the outlet end of thenozzle. Frequently, the air-curtain apparatus must be disposed at somedistance from the plane of the opening (FIG. 21) to, say, permit thepassage of a sliding door or the like between the nozzle 4 of theapparatus and the opening. In this case, we prefer to dispose a sealingplate 11 between the nozzle 4 and the wall 7. This plate functions fullyas effectively as the packings 1G and 16' described above.

Although the sealing means 10, 10' and 11, illustrated in FIGS. 1821,effectively prevent the accumulation of stagnant air between the nozzles4, 4 and the wall 7, we have found that the use of such sealing meansalong the elongated mouth of the nozzle, liable to encumber theapparatus and to prevent needed adjustment of the angle 5, may bedispensed with if suction or Venturi means are provided on the nozzle todraw any air present in the gap into the main air-curtain streams. Thus,the nozzle 4 of the apparatus illustrated in FIG. 8 is provided with asuction tube whose upper extremity 12 terminates in the gap between thenozzle 4 and the Wall 7 while its lower extremity 13 opens downwardly inthe nozzle 4. At least part of the secondary circulation 9 is, as aconsequence of the Venturi effect at the extremity 13 of the tube, drawninto the other end 12 of this tube, thereby preventing stagnation of anyair in the gap.

In FIG. 9 we show another air-curtain apparatus wherein the nozzle 4" isswivelable about a longitudinal axis on its ball-and-socket joint 15relatively to the plenum chamber 3 whereby the angle ,8 included betweenthe nozzle and the wall 7 (FIGS. 18-21) may be adjusted to provideoptimum results as previously noted. To lock the nozzle in its optimumangular position, it is formed with a link 16 having an arcuate slotengaged by a locking screw afiixed to the Wall 7. In this embodiment thenozzle 4 has an Opening at its upper end communicating with the gapbetween the nozzle and the wall 7 and is formed internally with a plate14' terminating at the upper nozzle opening whereby air is sucked by aVenturi effect from the gap into the nozzle as indicated by thebrokenline arrows.

A more convenient method of mounting the air-curtainproducing apparatusso that its nozzle angle is adjustable is shown in FIG. 10. The plenumchamber 3 and its nozzle portion 4 are pivoted at a hinge 17 to the wall7 while a turnbuckle 18, interconnecting the apparatus and the wall, isdisposed above the hinge 17 so that the angle {3 may be increased bydecreasing the effective length of the turnbuckle 13 and vice versa.

FIG. 11 illustrates an apparatus mounted in accordance with anotherembodiment of the invention wherein the angle [3 between the wall 7 andthe nozzle 4 of the apparatus is substantially 0 and the complementaryangle or is substantially 90. The impact-receiving surface 6 directlybelow the nozzle 4 is formed with a slotted or otherwise apertured plate19 which covers a depression 21 in the surface 6. In this depression,which is formed with upwardly diverging walls, there is disposed anairguiding cylinder with its axis substantially parallel to the nozzle4- whereby the air-curtain stream entering the depression is deflectedslopingly upwardly and outwardly from the substantially planar curtain.

In FIG. 12 we show an air-curtain-producing arrangement wherein an axialblower 2 feeds a plenum chamber which, in contradistinction to theplenum-chamber housing 162 (FIG. 1) of cylindrical configurationthroughout its length, has a turbulence-suppressing cylindricalantechamber 22 flanged at 25 to the angularly adjustable flareddistributing portion 23 of the plenum chamber 3. The distributingportion 23 is formed with a generally C-shaped nozzle outlet whoseelongated intermediate portion extends parallel to the plane of theopening 1 and emits a downwardly directed main air-curtain stream of thetype shown at 5 in FIGS. 18-21. The side portions 4a, 4b of the outletextend transversely to the elongated main portion dc thereof and formlateral air curtains which enclose the sides of the space of triangularcrosssection between the main air-curtain stream and the plane of theopening. The width of the lateral air curtains may be adjusted with theaid of a pair of lateral regulators 8 hinged to the plenum-chamberhousing.

Instead of having axial blowers or fans disposed at one or bothlongitudinal extremities of the apparatus as shown in FIGS. l-7 and 12,the cylindrical plenum-chamber housing 28 in FIGS. 13 and 14 is equippedwith a centrifugal blower 26 whose outlet communicates with the plenumchamber 3 at a central location, the chamber 3 being provided withdeflecting guides 27 to direct the incoming air stream toward each endof the chamber, thereby equalizing the outlet flow velocity along thenozzle 4 of the chamber.

FIG. 15 shows two centrifugal blowers 26 axially supplying air to thecylindrical housing 28 whose plenum chamber 3 contains a plurality oflaterally offset baflles 27, generally similar to the bafiles 133a to133d of FIGS. 2 and 3, at each side of the chamber to render thevelocity of the outgoing air substantially uniform over the length ofthe nozzle.

In FIGS. 16 and 17 we show another embodiment wherein a centrifugalimpeller 29, driven by a motor 31, is journaled in the housing 28 withits axis parallel to that of the housing but oifset therefrom wherebyair may be sucked into the plenum chamber 3 thereof via the longitudinalslot 30 in housing 28 and expelled via the longitudinally extendingnozzle 4 parallel to that slot.

A particularly advantageous construction of the generally cylindricalplenum chamber described above is shown in FIGS. 22 and 23. Thecylindrical housing 58, surrounding a plenum chamber 53, merges into atangential nozzle 54 which extends substantially parallel to the axis ofhousing 58 and is formed by a pair of spaced longitudinal panels 54',54". At the junction between the inner panel 54' and the housing 58 weprovide a relatively narrow longitudinally extending flap 55 (e.g.

of a width equal to about that of the spacing between the plates 54,54") which is bent inwardly and includes an angle between substantially20 and 40 with the plane of panel 54. The flap 55 has been found toreduce turbulence in the nozzle 54 as the air, under the high,substantially static pressure in the. chamber, enters the nozzle. 1

In order to adjust the outflow from nozzle 54 to eliminate anysubstantial deviation of the flowfrom a portion of the nozzle rout ofthe main air-curtain sheet of air and to reduce, any remaining variationin the velocity of the air at diiferent locations along the nozzle, weprovide an array of relatively closely spaced, individually adjustabledampers 56 extending between the main panels 5d, 54" tranversely to thelatter at the mouth of the nozzle. The dampers, of a length equal to afraction (preferably about one quarter) of the effective height of p thenozzle as seen in FIG. 23, may be frictionally engaged by the panels or,as shown in FIGS. 22 and 23, pivoted on their pins 57. The latter carryratchet wheels 58' respectively engaged by manually retractable pawls 59to hold the bafiles 56 in the positions to which they are set. Thedampers 56 are, advantageously, spaced apart by distances approximatelyequal to their length.

In FIGS. 24 and 25 we show two air-curtain-producing units 201 and 201",each generally similar to the apparatus 101 illustrated in FIG. 1, whosenozzles extend longitudinally along opposite lateral edges of an opening1 and direct respective air-curtain streams 265', 205 toward the medianplane of the opening. The major portion 266 of the air stream merging atthe median plane flows away from the cold chamber 207 while secondarycirculations 2%99 (similar to the circulation 9 previously described)are established between the opening 1 and the nozzles which areinclined, as before, at the angles 5 to the plane of the opening. Sincethe air curtain shielding the opening 1 must withstand larger cold-aircurrents at the base of the opening than at its top, we design thebaffles (which are generally similar to the bafiles 133a-133d) of theunits 201', 201 so that the velocity V of the air curtain at the base ofthe opening 1 is from 10 to greater than the velocity V of the aircurtain at the top of the opening.

FIGS. 26 and 27 illustrate another air-curtain-pro ducing arrangementaccording to our invention wherein an intake head 305 containing anaxial blower of the type housed in the head 195 (FIG. l) is flanged toan intermediate plenum-chamber housing 320' which, together with anotherhousing 320" flanged to the main cylindrical housing 328, produceslateral air curtains at each side of the principal air curtain aspreviously described. For this purpose, the housings 3219' 320" encloseextensions of the main plenum chamber and have nozzles 3521', 321 whichextend perpendicularly to the longitudinal nozzle 354 that lies parallelto the upper edge of the doorway 1. We have found that it is possible toincrease the efficiency of the air-curtain screen, especially forrelatively high openings, by providing a mechanical barrier, at least atthe lower part of the opening, between the cool-air chamber and thesecondary circulation balancing the convection-current outflow from thischamber. Advantageously, the mechanical barrier may comprise resilientlydefiectable sheet means, e.g., of rubber, interposed between the mainair curtain and the cold chamber and extending over a substantialportion of the doorway from its base. The sheet means may comprise apair of swinging rubber doors 33d, 33%" mounted along the lateral edgesof the doorway (FIGS. 26 and 27) upon vertical rods 331', 331 so as tobe defiectable by a cart or the like thrust through the doorway into thdot-dash position and, upon passage of the cart therethrough, to swingback to their solid-line position.

In FIG. 28 we show another air-curtaim-producing apparatus having anaxial fan 2, of the type shown in FIGS. 8-11, which feeds a downwardlyflared plenum chamber 3 and its elongated nozzle 4. The latter isadjustable, e.g. as illustrated in FIG. 9, about a longitudinal pivotand is bracketed by a pair of lateral air-curtain nozzles 8' Which areadjustable about respective transverse pivots. The nozzles 8 producelateral air screens which enclose, together with the main air screen,the space of triangular cross-section between the latter and the planeof the open ing 1 as described hereinabove. A plurality ofvelocityequalizing and distributing batlles 27a are spacedly positionedin the plenum chamber 3 to direct the air stream substantially uniformlyto the nozzles 4 and 8'.

FIGS. 29 and 30 of the drawing show another apparatus, generally similarto the one illustrated in FIG. 28 but with the curved baliies 27a of thelatter replaced by the planar 'bafiles 27b.

The construction of the apparatus may of course be modified withoutdeparting from the scope of the invention as defined by the appendedclaims. Thus, for example, some of the features herein disclosed willalso be useful where the air leaves the plenum chamber by a plurality ofaxially spaced lateral outlets rather than by a continuous slot.

What is claimed is:

l.'An apparatus for producing an air curtain to screen a generallyrectangular door opening in an enclosure wall against penetration byconvection currents, comprising an elongated plenum chamber extendingsubstantially horizontally above said opening, lower means coupled withsaid plenum chamber for supplying air thereto,van elongated nozzle onsaid plenum chamber communicating with the interior therewith, saidnozzle having a pair of longitudinally extending parallel panelsinclined with respect to said wall at an angle between substantially l5and 25 for producing an air current across said opening downwardlydiverging from said wall at said angle, said panels forming between theman air-outlet slot extending substantially over the full width of saidopening and tacing a floor surface near the bottom of said opening, oneof said panels lying closer than the other to said wall, and sealingmeans between said one of said panels and said wall above the lower edgeof said one or said panels forming a reflecting surface for upwardlycirculating air branched off said air current at said floor surface,said one of said panels being provided with air-entrance means belowsaid reflecting surface for aspir'ating part of said upwardlycirculating air into said nozzle.

' 2. An apparatus for producing an air curtain to screen a generallyrectangular door opening in an enclosure wall against penetration byconvection currents, comprising an elongated plenum chamber extendingsubstantially horizontally above said opening, a source of air underpressure in said chamber, an elongated main nozzle on said plenumchamber communicating with the interior therewith, said nozzle having apair of longitudinally extending parallel panels inclined with respectto said Wall at an angle between substantially 15 and 25 for producing aprimary air current across said opening downwardly diverging from saidwall at said angle, said panels forming between them an air-outlet slotextending substantially over the full width of said opening and facing afloor sur face, and a pair of auxiliary nozzles disposed near the endsof said main nozfle and bridging the space between said panels and saidwall, said auxiliary nozzles communicating with said source forproducing downwardly directed secondary air currents substantiallytransverse to said primary air current, thereby screening off threesides of a region of generally triangular cross-section adjacent saidopening.

3. A device for screening an opening in an enclosure Wall by an aircurtain, comprising a body of generally cylindrical configuration openon at least one of its ends, said body including a peripherally closedfirst section forming an antechamber next to said open end and a secondsection axially adjoining said first section, said second sectionforming a plenum chamber communicating with said antechamber and beingprovided along its side with nozzle means forming an outlet slot, saidslot communicating with the interior of said plenum chamber andextending over substantially its entire length, and a source of airunder pressure having a discharge end within said body ahead of saidopen end, said antechamber constituting a free space of sufiicientlength in axial direction to convert the stream of air entering saidplenum chamber from a turbulent state to substantially laminar flow.

4. A device according to claim 3, further comprising air-distributingmeans in said plenum chamber extending generally longitudinally thereofadjacent said nozzle for substantially equalizing the velocity of theoutgoing air flow along said slot.

5. A device according to claim 4 wherein said air-distributing meanscomprises a series of bafiles having transveresly spaced upstreamportions and laterally curved downstream portions directed toward saidnozzle, said upstream portions extending in longitudinal direction ofsaid plenum chamber, said downstream portions being relatively staggeredin longitudinal direction.

6. A device according to claim 5 wherein at least one of said bafilesterminates substantially at the junction of said plenum chamber withsaid free space.

7. A device for preventing the flow of air from a colder region to awarmer region through a door opening in a wall separating said regions,comprising a body on said wall above said door within said warmerregion, said body forming a generally cylindrical plenum chamberextending substantially horizontally across the width of said opening,and air-circulating means on said body having an intake in said warmerregion and a discharge end communieating with said plenum chamber; saidbody being provided with a slot forming a lateral air outlet for saidplenum chamber over substantially its entire length, said outlet beingtrained upon an opposite floor surfaced at a downward angle ofinclination relative to said wall at which the air current issuing fromsaid slot is split, upon impinging upon said floor surface, into a majorcomponent directed toward said warmer region and an oppositely directedminor component sufiicient to prevent the intrusion of air from saidcolder region along said floor surface, said major and minor componentsbeing related in substantially the ratio of 2: 1.

8. In a door-screening system comprising, in combination, a device forpreventing the fiow of air from a colder region to a Warmer regionthrough a door opening in a wall separating said regions, comprising abody on said wall above said door within said warmer region, said bodyforming a generally cylindrical plenum chamber extending substantiallyhorizontally across the width of said opening, and air-circulating meanson said body having an intake in said warmer region and a discharge endcommunicating with said plenum chamber; said body being provided with aslot forming a lateral outlet for said plenum chamber over substantiallyits entire length, said outlet being trained upon an opposite floorsurface at a downward angle of inclination relative to said wall atwhich the air current issuing from said slot is split upon impingingupon said floor surface, into a major component directed toward saidwarmer region and an oppositely directed minor component sufficient toprevent the intrusion of air from said colder region along said floorsurface, and swingable gate means at a lower portion of said dooropening extending over substantially less than the full height thereof.

9. A method of preventing the flow of air from a colder region to awarmer region through a door opening in a wall separating said regions,comprising the steps of creating a downwardly directed air curtainacross said opening toward a floor surface at the bottom thereof, saidair curtain diverging downwardly from said wall at an angle so chosen asto split said air curtain, upon its impingement on said floor surface,into a major component directed toward said warmer region and anoppositely dit2 rected minor component suflicient to prevent theintrusion of air from said colder region along said floor surface; andcompensating for changes in the temperature difference between saidregions by varying said angle to an extent maintaining the ratio of saidmajor and minor components at a value of substantially 2: 1.

10. A device for preventing the flow of air from a colder region to awarmer region through a door opening in a wall separating said regions,comprising a body on said wall above said door Within said warmerregion, said body forming a plenum chamber extending substantiallyhorizontally across the width of said opening, and aircirculating meanson said body having an intake in said Warmer region and a discharge endcommunicating with said plenum chamber; said body being provided with aslot forming a lateral air outlet for said plenum chamber oversubstantially its entire length, said outlet being trained upon anopposite floor surface at a downward angle of inclination relative tosaid wall at which the air current issuing from said slot is split, uponimpinging upon said floor surface, into a major component directedtoward said warmer region and an oppositely directed minor componentsufficient to prevent the intrusion of air from said colder region alongsaid floor surface, said major and minor components being related insubstantially the ratio of 2:1.

11. In a door-screening system, in combination, a device for preventingthe flow of air from a colder region to a warmer region through a dooropening in a wall separating said regions, comprising a body on saidwall above said door within said warmer region, said body forming aplenum chamber extending substantially horizontally across the width ofsaid opening, and air-circulating means on said body having an intake insaid warmer region and a discharge end communicating with said plenumchamber; said body being provided with a slot forming a lateral outletfor said plenum chamber over substantially its entire length, saidoutlet being trained upon an opposite floor surface at a downward angleof inclination relative to said wall at which the air current issuingfrom said slot is split, upon impinging upon said fioor surface, into afirst component directed toward said warmer region and an oppositelydirected second component opposing the intrusion of air from said colderregion along said fioor surface, said major and minor components beingrelated in substantially the ratio of 2: 1, and swingable gate means ata lower portion of said door opening extending over substantially lessthan the full height thereof.

12. A device for screening an opening in an enclosure wall by an aircurtain, comprising a body forming an elongated plenum chamber ofgenerally cylindrical configuration open on at least one of its ends andbeing provided along its side with nozzle means forming an outlet slot,said slot communicating with the interior of said plenum chamber andextending over substantially its entire length, and a source of airunder pressure having a discharge end within said body ahead of saidopen end, said discharge end being separated within said body from saidchamber by a free space of sufiicient length in axial direction toconvert the stream of air entering said plenum chamber from a turbulentstate to substantially laminar flow.

References Cited in the file of this patent UNITED STATES PATENTS

1. AN APPARATUS FOR PRODUCING AN AIR CURTAIN TO SCREEN A GENERALLYRECTANGULAR DOOR OPENING IN AN ENCLOSURE WALL AGAINST PENETRATION BYCONVECTION CURRENTS, COMPRISING AN ELONGATED PLENUM CHAMBER EXTENDINGSUBSTANTIALLY HORIZONTALLY ABOVE SAID OPENING, BLOWER MEANS COUPLED WITHSAID PLENUM CHAMBER FOR SUPPLYING AIR THERETO, AN ELONGATED NOZZLE ONSAID PLENUM CHAMBER COMMUNICATING WITH THE INTERIOR THEREWITH, SAIDNOZZLE HAVING A PAIR OF LONGITUDINALLY EXTENDING PARALLEL PANELSINCLINED WITH RESPECT TO SAID WALL AT AN ANGLE BETWEEN SUBSTANTIALLY 15AND 25* FOR PRODUCING AN AIR CURRENT ACROSS SAID OPENING DOWNWARDLYDIVERGING FROM SAID WALL AT SAID ANGLE, SAID